cmd/internal/gc: improve flow of input params to output params
This includes the following information in the per-function summary:
outK = paramJ encoded in outK bits for paramJ
outK = *paramJ encoded in outK bits for paramJ
heap = paramJ EscHeap
heap = *paramJ EscContentEscapes
Note that (currently) if the address of a parameter is taken and
returned, necessarily a heap allocation occurred to contain that
reference, and the heap can never refer to stack, therefore the
parameter and everything downstream from it escapes to the heap.
The per-function summary information now has a tuneable number of bits
(2 is probably noticeably better than 1, 3 is likely overkill, but it
is now easy to check and the -m debugging output includes information
that allows you to figure out if more would be better.)
A new test was added to check pointer flow through struct-typed and
*struct-typed parameters and returns; some of these are sensitive to
the number of summary bits, and ought to yield better results with a
more competent escape analysis algorithm. Another new test checks
(some) correctness with array parameters, results, and operations.
The old analysis inferred a piece of plan9 runtime was non-escaping by
counteracting overconservative analysis with buggy analysis; with the
bug fixed, the result was too conservative (and it's not easy to fix
in this framework) so the source code was tweaked to get the desired
result. A test was added against the discovered bug.
The escape analysis was further improved splitting the "level" into
3 parts, one tracking the conventional "level" and the other two
computing the highest-level-suffix-from-copy, which is used to
generally model the cancelling effect of indirection applied to
address-of.
With the improved escape analysis enabled, it was necessary to
modify one of the runtime tests because it now attempts to allocate
too much on the (small, fixed-size) G0 (system) stack and this
failed the test.
Compiling src/std after touching src/runtime/*.go with -m logging
turned on shows 420 fewer heap allocation sites (10538 vs 10968).
Profiling allocations in src/html/template with
for i in {1..5} ;
do go tool 6g -memprofile=mastx.${i}.prof -memprofilerate=1 *.go;
go tool pprof -alloc_objects -text mastx.${i}.prof ;
done
showed a 15% reduction in allocations performed by the compiler.
Update #3753
Update #4720
Fixes #10466
Change-Id: I0fd97d5f5ac527b45f49e2218d158a6e89951432
Reviewed-on: https://go-review.googlesource.com/8202
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/test/escape_struct_param2.go b/test/escape_struct_param2.go
new file mode 100644
index 0000000..c10c336
--- /dev/null
+++ b/test/escape_struct_param2.go
@@ -0,0 +1,298 @@
+// errorcheck -0 -m -l
+
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test escape analysis for struct function parameters.
+// Note companion strict_param1 checks *struct function parameters with similar tests.
+
+package notmain
+
+var Ssink *string
+
+type U struct {
+ _sp *string
+ _spp **string
+}
+
+type V struct {
+ _u U
+ _up *U
+ _upp **U
+}
+
+func (u U) SP() *string { // ERROR "leaking param: u to result ~r0 level=0$"
+ return u._sp
+}
+
+func (u U) SPP() **string { // ERROR "leaking param: u to result ~r0 level=0$"
+ return u._spp
+}
+
+func (u U) SPPi() *string { // ERROR "leaking param: u to result ~r0 level=1$"
+ return *u._spp
+}
+
+func tSPPi() {
+ s := "cat" // ERROR "moved to heap: s$"
+ ps := &s // ERROR "&s escapes to heap$"
+ pps := &ps // ERROR "tSPPi &ps does not escape$"
+ pu := &U{ps, pps} // ERROR "tSPPi &U literal does not escape$"
+ Ssink = pu.SPPi()
+}
+
+func tiSPP() {
+ s := "cat" // ERROR "moved to heap: s$"
+ ps := &s // ERROR "&s escapes to heap$"
+ pps := &ps // ERROR "tiSPP &ps does not escape$"
+ pu := &U{ps, pps} // ERROR "tiSPP &U literal does not escape$"
+ Ssink = *pu.SPP()
+}
+
+// BAD: need fine-grained analysis to avoid spurious escape of ps
+func tSP() {
+ s := "cat" // ERROR "moved to heap: s$"
+ ps := &s // ERROR "&s escapes to heap$" "moved to heap: ps$"
+ pps := &ps // ERROR "&ps escapes to heap$"
+ pu := &U{ps, pps} // ERROR "tSP &U literal does not escape$"
+ Ssink = pu.SP()
+}
+
+func (v V) u() U { // ERROR "leaking param: v to result ~r0 level=0$"
+ return v._u
+}
+
+func (v V) UP() *U { // ERROR "leaking param: v to result ~r0 level=0$"
+ return v._up
+}
+
+func (v V) UPP() **U { // ERROR "leaking param: v to result ~r0 level=0$"
+ return v._upp
+}
+
+func (v V) UPPia() *U { // ERROR "leaking param: v to result ~r0 level=1$"
+ return *v._upp
+}
+
+func (v V) UPPib() *U { // ERROR "leaking param: v to result ~r0 level=1$"
+ return *v.UPP()
+}
+
+func (v V) USPa() *string { // ERROR "leaking param: v to result ~r0 level=0$"
+ return v._u._sp
+}
+
+func (v V) USPb() *string { // ERROR "leaking param: v to result ~r0 level=0$"
+ return v.u()._sp
+}
+
+func (v V) USPPia() *string { // ERROR "leaking param: v to result ~r0 level=1$"
+ return *v._u._spp
+}
+
+func (v V) USPPib() *string { // ERROR "leaking param: v to result ~r0 level=1$"
+ return v._u.SPPi()
+}
+
+func (v V) UPiSPa() *string { // ERROR "leaking param: v to result ~r0 level=1$"
+ return v._up._sp
+}
+
+func (v V) UPiSPb() *string { // ERROR "leaking param: v to result ~r0 level=1$"
+ return v._up.SP()
+}
+
+func (v V) UPiSPc() *string { // ERROR "leaking param: v to result ~r0 level=1$"
+ return v.UP()._sp
+}
+
+func (v V) UPiSPd() *string { // ERROR "leaking param: v to result ~r0 level=1$"
+ return v.UP().SP()
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s3
+func tUPiSPa() {
+ s1 := "ant"
+ s2 := "bat" // ERROR "moved to heap: s2$"
+ s3 := "cat" // ERROR "moved to heap: s3$"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "&s2 escapes to heap$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$" "moved to heap: ps4$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPa &ps2 does not escape$" "tUPiSPa &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "&ps4 escapes to heap$" "&s3 escapes to heap$" "tUPiSPa &U literal does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&U literal escapes to heap$" "&ps6 escapes to heap$" "&s5 escapes to heap$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPa &V literal does not escape$" "tUPiSPa &u3 does not escape$"
+ Ssink = v.UPiSPa() // Ssink = &s3 (only &s3 really escapes)
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s3
+func tUPiSPb() {
+ s1 := "ant"
+ s2 := "bat" // ERROR "moved to heap: s2$"
+ s3 := "cat" // ERROR "moved to heap: s3$"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "&s2 escapes to heap$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$" "moved to heap: ps4$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPb &ps2 does not escape$" "tUPiSPb &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "&ps4 escapes to heap$" "&s3 escapes to heap$" "tUPiSPb &U literal does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&U literal escapes to heap$" "&ps6 escapes to heap$" "&s5 escapes to heap$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPb &V literal does not escape$" "tUPiSPb &u3 does not escape$"
+ Ssink = v.UPiSPb() // Ssink = &s3 (only &s3 really escapes)
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s3
+func tUPiSPc() {
+ s1 := "ant"
+ s2 := "bat" // ERROR "moved to heap: s2$"
+ s3 := "cat" // ERROR "moved to heap: s3$"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "&s2 escapes to heap$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$" "moved to heap: ps4$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPc &ps2 does not escape$" "tUPiSPc &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "&ps4 escapes to heap$" "&s3 escapes to heap$" "tUPiSPc &U literal does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&U literal escapes to heap$" "&ps6 escapes to heap$" "&s5 escapes to heap$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPc &V literal does not escape$" "tUPiSPc &u3 does not escape$"
+ Ssink = v.UPiSPc() // Ssink = &s3 (only &s3 really escapes)
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s3
+func tUPiSPd() {
+ s1 := "ant"
+ s2 := "bat" // ERROR "moved to heap: s2$"
+ s3 := "cat" // ERROR "moved to heap: s3$"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "&s2 escapes to heap$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$" "moved to heap: ps4$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPd &ps2 does not escape$" "tUPiSPd &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "&ps4 escapes to heap$" "&s3 escapes to heap$" "tUPiSPd &U literal does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&U literal escapes to heap$" "&ps6 escapes to heap$" "&s5 escapes to heap$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPd &V literal does not escape$" "tUPiSPd &u3 does not escape$"
+ Ssink = v.UPiSPd() // Ssink = &s3 (only &s3 really escapes)
+}
+
+func (v V) UPiSPPia() *string { // ERROR "leaking param: v to result ~r0 level=2$"
+ return *v._up._spp
+}
+
+func (v V) UPiSPPib() *string { // ERROR "leaking param: v to result ~r0 level=2$"
+ return v._up.SPPi()
+}
+
+func (v V) UPiSPPic() *string { // ERROR "leaking param: v to result ~r0 level=2$"
+ return *v.UP()._spp
+}
+
+func (v V) UPiSPPid() *string { // ERROR "leaking param: v to result ~r0 level=2$"
+ return v.UP().SPPi()
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s4
+func tUPiSPPia() {
+ s1 := "ant"
+ s2 := "bat"
+ s3 := "cat"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "tUPiSPPia &s2 does not escape$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPPia &ps2 does not escape$" "tUPiSPPia &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "tUPiSPPia &U literal does not escape$" "tUPiSPPia &ps4 does not escape$" "tUPiSPPia &s3 does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&ps6 escapes to heap$" "&s5 escapes to heap$" "tUPiSPPia &U literal does not escape$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPPia &V literal does not escape$" "tUPiSPPia &u3 does not escape$"
+ Ssink = v.UPiSPPia() // Ssink = *&ps4 = &s4 (only &s4 really escapes)
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s4
+func tUPiSPPib() {
+ s1 := "ant"
+ s2 := "bat"
+ s3 := "cat"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "tUPiSPPib &s2 does not escape$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPPib &ps2 does not escape$" "tUPiSPPib &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "tUPiSPPib &U literal does not escape$" "tUPiSPPib &ps4 does not escape$" "tUPiSPPib &s3 does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&ps6 escapes to heap$" "&s5 escapes to heap$" "tUPiSPPib &U literal does not escape$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPPib &V literal does not escape$" "tUPiSPPib &u3 does not escape$"
+ Ssink = v.UPiSPPib() // Ssink = *&ps4 = &s4 (only &s4 really escapes)
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s4
+func tUPiSPPic() {
+ s1 := "ant"
+ s2 := "bat"
+ s3 := "cat"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "tUPiSPPic &s2 does not escape$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPPic &ps2 does not escape$" "tUPiSPPic &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "tUPiSPPic &U literal does not escape$" "tUPiSPPic &ps4 does not escape$" "tUPiSPPic &s3 does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&ps6 escapes to heap$" "&s5 escapes to heap$" "tUPiSPPic &U literal does not escape$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPPic &V literal does not escape$" "tUPiSPPic &u3 does not escape$"
+ Ssink = v.UPiSPPic() // Ssink = *&ps4 = &s4 (only &s4 really escapes)
+}
+
+// BAD: need fine-grained (field-sensitive) analysis to avoid spurious escape of all but &s4
+func tUPiSPPid() {
+ s1 := "ant"
+ s2 := "bat"
+ s3 := "cat"
+ s4 := "dog" // ERROR "moved to heap: s4$"
+ s5 := "emu" // ERROR "moved to heap: s5$"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "tUPiSPPid &s2 does not escape$"
+ ps4 := &s4 // ERROR "&s4 escapes to heap$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$" "moved to heap: ps6$"
+ u1 := U{&s1, &ps2} // ERROR "tUPiSPPid &ps2 does not escape$" "tUPiSPPid &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "tUPiSPPid &U literal does not escape$" "tUPiSPPid &ps4 does not escape$" "tUPiSPPid &s3 does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "&ps6 escapes to heap$" "&s5 escapes to heap$" "tUPiSPPid &U literal does not escape$"
+ v := &V{u1, u2, &u3} // ERROR "tUPiSPPid &V literal does not escape$" "tUPiSPPid &u3 does not escape$"
+ Ssink = v.UPiSPPid() // Ssink = *&ps4 = &s4 (only &s4 really escapes)
+}
+
+func (v V) UPPiSPPia() *string { // ERROR "leaking param: v to result ~r0 level=3$"
+ return *(*v._upp)._spp
+}
+
+// This test isolates the one value that needs to escape, not because
+// it distinguishes fields but because it knows that &s6 is the only
+// value reachable by two indirects from v.
+// The test depends on the level cap in the escape analysis tags
+// being able to encode that fact.
+func tUPPiSPPia() { // This test is sensitive to the level cap in function summary results.
+ s1 := "ant"
+ s2 := "bat"
+ s3 := "cat"
+ s4 := "dog"
+ s5 := "emu"
+ s6 := "fox" // ERROR "moved to heap: s6$"
+ ps2 := &s2 // ERROR "tUPPiSPPia &s2 does not escape$"
+ ps4 := &s4 // ERROR "tUPPiSPPia &s4 does not escape$"
+ ps6 := &s6 // ERROR "&s6 escapes to heap$"
+ u1 := U{&s1, &ps2} // ERROR "tUPPiSPPia &ps2 does not escape$" "tUPPiSPPia &s1 does not escape$"
+ u2 := &U{&s3, &ps4} // ERROR "tUPPiSPPia &U literal does not escape$" "tUPPiSPPia &ps4 does not escape$" "tUPPiSPPia &s3 does not escape$"
+ u3 := &U{&s5, &ps6} // ERROR "tUPPiSPPia &U literal does not escape$" "tUPPiSPPia &ps6 does not escape$" "tUPPiSPPia &s5 does not escape$"
+ v := &V{u1, u2, &u3} // ERROR "tUPPiSPPia &V literal does not escape$" "tUPPiSPPia &u3 does not escape$"
+ Ssink = v.UPPiSPPia() // Ssink = *&ps6 = &s6 (only &s6 really escapes)
+}
